FXUS63 KIWX 240003
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
703 PM EST WED DEC 23 2009
.UPDATE...
GRIDS IN DECENT SHAPE AT THIS POINT...BUT ADVISORY NEEDED SOME
CHANGES TO UPDATED ZONES AND WSW FORTHCOMING.
OVERALL COVERAGE OF PRECIP HAS BEGUN TO DIMINISH SOMEWHAT BUT
POCKETS OF HIGHER RETURNS INDICATIVE OF POCKETS OF SLEET AND
FREEZING RAIN ARE STILL SHOWN. AS EXPECTED...AFTER THE INITIAL
BAND OF MIXED PRECIP THAT HAS MOVED ACROSS NEARLY ALL OF THE CWA
AT SOME POINT...THE BEST COVERAGE HAS BECOME MORE CONFINED TO WEST
OF INTERSTATE 69 AND ESPECIALLY ALONG AND WEST OF STATE ROUTE 15
ACROSS INDIANA. NUMEROUS REPORTS OF SLIDE-OFFS AND LIGHT GLAZING
HAS BEEN REPORTED ACROSS THE PREVIOUS ADVISORY AREA. OUTSIDE OF
THE HIGHER RETURNS...SOME FREEZING DRIZZLE IS STILL BEING SEEN AND
UPSTREAM OBSERVATIONS AND RADAR DATA OUT OF ILLINOIS SHOWS THIS
MAY CONTINUE INTO THE EVENING. TO HELP COVER ANY EVENING TRAVEL
AND PREVIOUS HEADLINES OUT TILL 6Z...HAVE EXTENDED PORTIONS OF THE
ADVISORY THAT WERE SET TO EXPIRE AT 00Z TO 6Z. HAVE ALSO EXPANDED
THE ADVISORY ONE TIER EAST TO COVER REPORTS OF SOME ICING ON
SURFACES. SUSPECT THAT COUNTIES WILL BE ABLE TO BE DROPPED PRIOR
TO THE EXPIRATION ESPECIALLY EAST...BUT WITH STRENGTH OF LIFT AND
OBVIOUS CONTINUED FEED OF MSTR...DON'T WANT TO CUT THINGS OFF TOO
PREMATURE.
AFTER MIDNIGHT...STEADIER PRECIP MAY MOVE BACK IN TO FAR WESTERN
AREAS...BUT WILL REEVALUATE THINGS IN A FEW HOURS.
&&
.AVIATION /00Z TAFS/...
TRICKY TAFS FOR MUCH OF THE PERIOD...ESPECIALLY AT KSBN. LARGE
AREA OF WAA PRECIP HAS PERSISTED ACROSS THE KSBN AREA FOR SEVERAL
HOURS WITH PRECIP NOW HAVING TRANSITIONED TO MAINLY FREEZING RAIN
OR SLEET AS SFC TEMPS REMAIN BELOW FREEZING. GIVEN UPSTREAM OBS
AND RADAR IMAGES...WILL CONTINUE WITH FREEZING PRECIP MENTION FOR
A FEW HOURS THEN TAPER OFF TO MORE OF A TEMPO GROUP THROUGH 6Z.
AMENDMENTS MAYBE NEEDED AS RADAR DATA BACK ACROSS SW ILLINOIS
SHOWS A LARGE AREA OF ADDITIONAL PRECIP THAT COULD ROTATE INTO THE
AREA LATER TONIGHT. HOWEVER MODELS KEEP THIS JUST WEST OF THE
AIRPORT. AT KFWA WILL GO WITH TEMPO GROUP FOR A FEW HOURS TO
HANDLE WHAT WILL LIKELY TRANSITION TO MORE OF A FREEZING DRIZZLE
SETUP THIS EVENING. CONDITIONS WILL PROBABLY BE DRY INTO THE OVER
NIGHT HOURS AND MUCH OF CHRISTMAS EVE.
AFTER 18Z...HEAVIER PRECIP WILL BEGIN TO ARRIVE AT KSBN WITH SFC
TEMPS IN QUESTIONS BUT LIKELY NEAR OR JUST BELOW FREEZING. AS A
RESULT HAVE WENT PREDOMINANT LIGHT FREEZING RAIN FOR NOW WITH
FURTHER CHANGES LIKELY. ADDITIONAL PRECIP MAY HOLD OFF AT KFWA
UNTIL AFTER THE VALID TIME.
&&
.PREV DISCUSSION... /ISSUED 407 PM EST WED DEC 23 2009/
SHORT TERM...
INITIAL BAND OF WAA PRECIP ASSOCIATED WITH DEEPENING SFC LOW OVER
THE SRN PLAINS WAS MOVG ACROSS THE CWA THIS AFTN. ZR BEING REPORTED
A LITTLE FARTHER NE THAN PREVIOUS ADVISORY AREA, SO HAVE EXPANDED
ADVISORY NE A COUPLE OF COUNTIES IN NORTH CENTRAL INDIANA AND
SOUTHWEST MICHIGAN FOR THIS EVENING. SHOULD BE A LULL IN THE PRECIP
AS STRONGER WAA SHIFTS TO THE NW OF OUR CWA AS LOW CONTS TO
INTENSIFY...HOWEVER...SOME LIGHT FREEZING RAIN MAY PERSIST ALONG OUR
WRN BORDER LATE TONIGHT AND INTO THU MORNING. FOR NOW CONTD WITH
ENDING TIME OF ADVISORY AT 1AM BUT THIS MAY NEED TO BE EXTENDED OVER
NW INDIANA.
COLD FRONT ASSOCIATED WITH VERY STRONG PLAINS LOW WILL APPROACH THE
CWA FROM THE SW ON THURSDAY. CONTINUED EASTERLY SFC WINDS WILL LIMIT
WARMUP AHEAD OF THE CDFNT AS SGFNT BAND OF RAIN MOVES TOWARD THE
AREA. STILL APPEARS THAT INITIAL RAINFALL WITH THIS HEAVIER BAND OF
PRECIP MAY OCCUR INTO FREEZING SFC TEMPS OVER NRN PORTIONS OF THE
CWA LATE THU/THU EVE, BEFORE WAA RAISES TEMPS ABOVE FREEZING. THUS,
HAVE CONTINUED WITH A WINTER STORM WATCH FOR THU AFTN/NGT WHERE
PREVIOUSLY ISSUED ACROSS SRN MI AND FAR NRN INDIANA, THOUGH AT THIS
POINT SEEMS MORE LIKELY THAT EVENTUAL HEADLINE WILL BE FOR AN
ADVISORY RATHER THAN WARNING DUE TO SHORT DURATION OF SUB-FREEZING
TEMPS DURING THE WATCH PERIOD. ADDED MENTION OF HEAVY RAIN THU NGT
AS STRONG FORCING COMBINED WITH GULF MOISTURE ADVECTING INTO THE
AREA AHEAD OF THIS SYSTEM'S COLD FRONT SHOULD RESULT IN A PERIOD OF
HEAVY RAIN. APPEARS THIS WILL MOVE THROUGH THE AREA QUICKLY ENOUGH
THAT FLOODING WILL NOT BE A CONCERN.&&
LONG TERM...
FRIDAY THROUGH WEDNESDAY...FOR THIS PACKAGE...FAVOR A BLEND OF THE
SLOWER CANADIAN GEM AND THE OPERATIONAL ECMWF. THESE MODELS ARE
SLOWER THEN THE GFS ENSEMBLE MEAN. THE GFS APPEARS TO BE SHOWING THE
TYPICAL BIAS OF TRYING TO EJECT THIS TYPE OF SYSTEM EAST TOO FAST.
THERE WILL BE A RATHER COMPLEX FUJIWHARA INTERACTION OF 2 UPPER
LEVEL SYSTEMS FRIDAY. THE MOIST CONVEYOR BELT OF WARM AIR WILL BE
COMPLETELY CUT OFF AS THE SYSTEM BECOMES OCCLUDED. THE DRY SLOT
SHOULD BE MOVING INTO THE AREA FRIDAY MORNING WITH THE HEAVIEST
PRECIPITATION NORTHEAST OF THE AREA. TEMPERATURES SHOULD WARM TO
AROUND 40F OVER MOST OF THE AREA BEFORE THE COLD FRONT MOVES IN FROM
THE SOUTHWEST. SOME CONCERN EXISTS FOR FLOODING FROM OVERNIGHT
RAINFALL AMOUNTS THURSDAY NIGHT PLUS SNOWMELT FRIDAY. THE RAINFALL
COMBINED WITH SNOW MELT WILL LIKELY BRING RISES TO AREA RIVERS
FRIDAY. AT THIS TIME...FEEL POTENTIAL FLOOD ISSUES WILL BE MAINLY
AREA RIVER RISES...BUT ISOLATED FLOODING OF LOW AREAS ARE
POSSIBLE...ESPECIALLY IF STORM DRAINS BECOME PLUGGED BY DEBRIS OR
MELTING SNOW AND ICE. MUCH COLDER CONDITIONS WILL OCCUR EARLY FRIDAY
NIGHT WITH FLASH FREEZING LIKELY. THE UPPER LOW SHOULD THEN EJECT
OUT OVER THE FORECAST AREA OVER THE WEEKEND. HAVE RAISED SNOW
CHANCES TO HIGH CHANCE. GIVEN THIS PATTERN...BELIEVE THERE WILL
PROBABLY BE ANOTHER 1-4 INCHES OF SNOW OVER THE WEEKEND BASED ON THE
DURATION OF LIGHT SNOW. THE POTENTIAL FOR LAKE EFFECT SNOW LOOKS
MARGINAL EARLY...BUT SHOULD INCREASE LATE IN THE PERIOD AS WINDS
BECOME NORTHWEST. HAVE INDICATED THIS POTENTIAL WITH A CHANCE FOR
LAKE EFFECT SNOW SUNDAY NIGHT THROUGH MONDAY NIGHT.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
MORNING FOR INZ003>007.
WINTER WEATHER ADVISORY UNTIL 1 AM EST /MIDNIGHT CST/ THURSDAY
FOR INZ003>005-012>016-020-022.
WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR
INZ023>027-032>034.
MI...WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
MORNING FOR MIZ077>081.
WINTER WEATHER ADVISORY UNTIL 1 AM EST THURSDAY FOR MIZ077-078.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 7 AM EST THURSDAY FOR LMZ043-046.
GALE WARNING FROM 7 AM THURSDAY TO 1 PM EST FRIDAY FOR LMZ043-
046.
&&
$$
SHORT TERM...JT
LONG TERM...SKIPPER
AVIATION...FISHER
UPDATE...FISHER
